Field of the Invention
The present invention relates to an optical apparatus that includes an optical system including a plastic lens, and particularly relates to a structure for holding the lens.
Description of the Related Art
A plastic lens is held by a holder such as a lens holding frame by, for example, engaging a protrusion (pin) integrally provided to the lens with a hole portion formed on the holder.
Japanese Patent Laid-open No. 2004-184787 discloses a structure including a plastic lens provided with four pins (first to fourth pins), and a holder provided with four hole portions (first to fourth hole portions) respectively corresponding to the four pins. The first pin has its entire circumference engaged with the first hole portion, and the fourth pin is inserted into the fourth hole portion as an elongated hole portion extending in a direction toward the first hole portion, thereby positioning the lens relative to the holder. The second and third pins are inserted into the second and third hole portions having inner diameters larger than outer diameters of the second and third pins. Then, heads of the first to third pins inserted into the first to third hole portions are melted by thermal caulking, and thereby the lens and the holder are fixed.
Japanese Patent Laid-open No. 04-240608 discloses a structure including a plastic lens provided with three pins (first to third pins), and a holder provided with three hole portions (first to third hole portions) respectively corresponding to the three pins. The first to third hole portions are each formed as an elongated hole portion extending in a lens radial direction from an optical axis. The first to third pins are respectively inserted into the first to third hole portions with their displacement in the lens radial direction being allowed, and thereby the lens is held by the holder. The lens is fixed to the holder by being pressed to the holder by an end of an elastic member whose another end is in contact with a fixed member.
However, in the structure disclosed in Japanese Patent Laid-open No. 2004-184787, a difference between linear expansion coefficients of the lens and the holder that are formed of materials different from each other may cause, for example, the lens to expand more largely than the holder due to an increase in an ambient temperature. In this case, the structure does not allow the lens with its first to third pins fixed to the holder by the thermal caulking to compensate an expansion force in its lens radial direction orthogonal to its optical axis direction. Thus, the lens expands in the optical axis direction. This expansion of the lens in the optical axis direction may cause a change of a curvature of its lens surface and a distortion thereof, which degrades an optical performance.
On the other hand, in the structure disclosed in Japanese Patent Laid-open No. 04-240608, all the first to third hole portions (elongated hole portions) formed in the holder allow the first to third pins provided to the lens to be displaced in the lens radial direction. With this configuration, the problem with the structure disclosed in Japanese Patent Laid-open No. 2004-184787 can be avoided. However, positioning the lens relative to the holder without gaps in the structure disclosed in Japanese Patent Laid-open No. 04-240608 requires significantly rigorous accuracies on a phase relation between the first to third pins of the lens and the first to third hole portions of the holder and on a relation between the outside diameters of the pins and widths of the elongated hole portions, which makes manufacturing of such a structure difficult.